PSVIII-B-12 Impact of Ruminal Acidosis on Cattle Energy Metabolism

The objective of this study was to determine the impact of a bout of ruminal acidosis on gas emissions of cattle unadapted to a high concentrate diet. Eleven ruminally cannulated steers (body weight = 352 kg ± 27) were blocked into 3 groups based on initial body weight. Prior to the start of the experiment, animals were consuming a forage-based diet as well as adapted to the headbox style respiration chambers. Additionally, prior to the experiment, gas emission data were collected over a 24-hour period when cattle received an ad libitum forage-based diet for use as a covariate in the statistical analysis. For the experiment, steers were moved into headboxes at the conclusion of a 24 hour fast and subsequently received 1 of 2 treatment diets: control (CON), forage-based diet or acidosis (ACID), concentrate-based diet. Steers remained in the headboxes for 48 hours. Gas concentrations from each headbox were collected hourly and analyzed with an infrared photoacoustic gas analyzer. Data were analyzed with the MIXED procedure of SAS 9.4. There was a tendency for a treatment × day effect (P = 0.09) with steers on the ACID treatment consuming 1.95 kg less on day 2 than CON steers. Dry matter intake was affected by day (P < 0.01) with steers consuming 4.35 kg less on day 2. There was an effect of treatment (P < 0.01) with CON steers having a greater ruminal pH than ACID steers. Steers on the ACID treatment had less CO2 emissions (P < 0.01) than CON steers, but there were no observed differences (P ≥ 0.19) in O2 emissions or respiratory quotient. Acidosis decreased dry matter intake and CO2 emissions but not O2 emissions for cattle unadapted to a high concentrate diet.